Electrical gaseous discharge device having constant starting characteristics



April 22, 1947. p, `W STUTSMAN 2,419,236 ELECTRICAL GAsECUs DISCHARGEDEVICE HAVING CONSTANT STARTING CHARACTERISTICS i E i P. W. STUTSMANApnl122, 1947. 2,419,236

.ELECTRICAL GASEOUS DISCHARGE DEVICE HAVING CONSTANT STARTINGCHARACTERISTICS Filed June 8, 1943- 2 Sheets-Sheet 2 Patented Apr. 22,1947 ELECTRICAL GASEOUS DISCHARGE DEVICE HAVING CONSTANT STARTING CHAR-ACTERISTICS a Paul W. Stutsman, Needham, Mass.. assignor, by

mesne assignments, to Raytheon Manufacturing Company, Newton, Mass., acorporation of Delaware Application June 8, 1943, Serial No. 490,094

6 Claims. (Cl. Z50-27.5)

. This invention relates to gaseous electric discharge devices,generally, and particularly to discharge devices of the cathode glowtype.

It is among the objects of the invention to provide a cathode glowdevice having constant electrical characteristics, and particularly sucha device having a constant break-down voltage, so that the same willstart at the same voltage and continue to break down at this startingvoltage throughout the life of the device.

A further object of the invention is to provide a device of this typewhich can be manufactured in quantity in such a manner that the devicesso constructed differ only slightly from each other in their electricalcharacteristics, and particularly with respect to the starting voltage,to the end that large circuit adjustments need not be made when onedevice is substituted for another in the same circuit The above andother objects and features of the invention will be made fully apparentto those skilled in the art from a consideration of the followingdetailed description taken in conjunction with the accompanying drawingswhich form a part hereof, and in which:

Fig. 1 shows in perspective, and with parts cut away to show internalstructure, a glow tube constructed in accordance with the presentinvention;

Fig. 2 shows a section taken along the line 2-2 of Fig. 1;k

Fig. 3 shows a perspective View on an enlarged scale of thecathodestructure;

Fig. 4 is a View similar to Fig. 1 of a modied form of the invention;

Fig. 5 shows in section and on an enlarged scale a portion of theelectrode structure of the modification shown in Fig. 4.

Referring to the drawings, and first to the form shown in Figs. l, 2 and3, there is shown a sealed envelope I, of glass or other suitablematerial, having a reentrant stem 2. Current lead-in wires 3 and 4,sealed in stem 2 by a press 5, provide connections between a suitablesource of power and electrodes 6 and 1.

In this form of the invention the electrodes and 1, which constitute,respectively, the cathode an anode of the discharge device, areconstructed in the form of concentric cylinders, the cathode B havingsomewhat less external diameter than the internal diameter of thecylindrical anode 7. The cathode 6 is formed of a ne Wire screen, whichscreen is supported and held in a cylindrical shape by a metal cap 8which is welded and otherwise securely attached to one end of thescreen, and by a similar cap 9 aiiixed to thev opposite end. The endcaps 8 and 9 are identical except that the lower end cap 9 is providedwith a central opening I li for purposes which will hereinafter be setforth. Each of the caps 8 and d is provided with diametrically opposednotched portions II and I2 for the purpose of permitting supporting rodsi3 and I4 to pass through the cathode structure.

The anode 'I is formed of a nickel sleeve of substantially the samelength as the overall length of the cathode 6, but of suciently greaterdiameter to provide a discharge space I5 therebetween. The anode 'I isalso provided with supporting rods Il and I8 which are welded orotherwise rigidly xed to its external surface on diametrically oppositesides thereof.

The cathode 6 and the anode 'I are held in properly spaced concentricrelation by means of mica plates I9 and 20 which close or partiallyclose the upper and lower ends of the electrodes E and 'l and throughwhich the rods I2, I3, I'I and li! project. The mica plates I9 and 20are substantially identical except that the lower plate has a centralopening 2l registering with the opening IIJ in the base capA 9 of thecathode 6. Tabs 22 welded to the projecting ends of the rods I2, I3, I'Iand I8, above the mica plate I9 and below the lower mica plate 20,prevent relative movement of the cathode and anode in a longitudinaldirection, thus providing a unitary cathode and anode structure whichmay be assembled as a unit prior to the mountingl of same upon thesupporting structure.

Lead-in wire 3 is connected to support rod I3 of the cathode, while thelead-in wire 4 is bent to connect with the rod I8 of the anode. Thuslead-in connections 3 and d support the cathode and anode structure aswell as provide connections to a suitable source of power. A pair oflead-in wires 23 and 24 also sealed in the stem 2 by the press 5 extendthrough the opening 2| in the mica plate 2t and provide a support for agetter 25, which getter is welded or otherwise suitably fixed to thewires 23 and 24 at its opposite ends and projects upwardly through theopening I0 in the base cap 9 into the hollow interior of the cathode 6.The getter 25 serves not only to clean up the gases remaining in theenvelope I after the evacuation thereof but also serves to activate aportion of the cathode, as will be hereinafter more fully described.

In the preferred Inode of manufacture of the device the cathode 6 isconstructed of nickel screen of about mesh and is oxidized in air andI4, is inserted in the cylindrical anode 1.-

'I'he mica disks I9 and 20 are each provided with two diametricallyopposite holes 26 to accommodate the projecting ends of rods I3 and I4,and two similarly diametrically opposite holes 2'I spaced farther towardthe circumference of the disk and preferably at 90 degrees from holes 26to accommodate the projecting ends of the rods I'I and I8. These disks,therefore, may be placed to close the ends of the cathode and anode, atthe edges thereof. This provides a combined cathode-anode assembly whichforms a rigid unitary structure and in which there can be no relativemovement, or displacement of the cathode relative to the anode. Thecathode-anode assembly is now mounted upon the stem 2 by welding leadinwire 3 to the projecting end of the supporting rod I3 0f cathode 5 andby welding lead-in wire 4 to the supporting rod IS of the anode 7. Inthis position the getter 25 projects upwardly through the opening 2I inthe mica plate 20 and through the opening lil in the end cap 9 of thecathode E so that the getter 25 extends into the interior of the hollowcathode 6. The assembled structure may now be inserted into the envelopeI, which may have an internal diameter such that the projecting points28 on the mica disks or plates I9 and 20l are in contact with the innerwall thereof, thereby minimizing vibration of said combinedcathode-anode structure. l

The envelope I is now evacuated, and preferably the electrode structureis heated by induction to assist in driving oif residual gases; getter25 contains an activating material, such as barium, which while aidingin cleaning up the gases remaining in the tube serves the furtherimportant function of rendering that portion of the cathode 6 which isexposed thereto more active than other portions. When the getter 25 isflashed, a material such as barium is released and is deposited uponthat portion of the cathode screen 6 between the end caps 8 and 9. Theend portions of the cathode beyond the flat faces of these end caps areshielded by these caps from the activating material. The electrodestructure is again heated by induction to the end that the temperatureof the cathode screen 6 is raised sufciently for the oxide surfacethereof to combine with and fix the getter and thereby activate thisportion of the screen.

By the above arrangement there is provided a discharge space I5 betweenthe cathode 6 and the anode 'I such that all points on the cathode areequidistant from the anode.

I have found that if a relatively large cathode area is spaced so thatthe effective distance between any point on this area and the nearestpoint on the anode is constant for all such points, then variations instarting potential are substantially reduced.

The effective distance between the cathode and the anode is altered atthe edges and ends of the electrodes by edge effects so that, tomaintain the constant effective distance between the active cathode areaand the anode, variations due to edge eiects must be prevented if aconstant starting potential is to be obtained.

In the form of the invention described the active cathode area isprovided by that portion of the cathode 6 between the end caps 3 and 9.The effective distance between any point on this cathode area and thenearest point on the anode 'I is constant for all such points.Variations in the effective distance between the points on the activearea of the cathode and the anode at the edges thereof are prevented inthis instance by providing an extension of the electrostatic fieldbetween the cathode and anode by an unactivated area of the cathodewhich extends beyond the activated area, but remains in the same spacedY relation to the anode. Activation of this area is Vl0 The preventedsince these end portions of the cathode are shielded from the activatingmaterial of the getter by the end caps B and 9.

The activated area of th* cathode is suiciently large to insure that theeffect of ionization due to external influences at any given instantwill be comparable to that during any other short period as measured inmicroseconds. Thus while in one portion of the space I5 there may beionization due to some transient at one instant, the

area is su'lciently large so that at some portion of the space thetransient conditions due to radiation and similar effects will besimilar at any subsequent instant so that variation of the breakdownpotential due to differences in these transients at dilerent instants isavoided.

I have also found that the electrical characteristics of the tube areimproved and constant starting potentials are assured if the equidistantspacing between the active portion of cathode and the anode, as abovedescribed, is made approximately equal to the minimum starting potentialdistance.

By minimum starting potential distance, I refer to the fact that if thetwo electrodes in a gaseous discharge device are moved relative to eachother there will be found a certain spacing at which, if all otherfactors remain constant, the starting voltage is at a minimum. If theelectrodes are moved closer together than this distance the startingpotential will be found to rise sharply. If moved farther apart thestarting potential also rises, but more gradually. Thus for any givenelectrode material in any given gas at a given pressure there may befound a spacing for the electrodes at which the starting potential is ata minimum.

While it is preferred that the distance between any point on the cathodeand the nearest point on the anode in the uniform field between' the twoelectrodes be substantially equal to the minimum starting potentialdistance, as above described, it will be understood that some of thebenefits of the invention may be attained at a somewhat greaterdistance, in which case the tube will start at a somewhat higherpotential if other factors are maintained constant. However, thedistance between the cathode and anode should not be substantially ofless than the mini- 'mum starting potential distance since in that casethe discharge will tend to seek paths between the cathode and the anodewhich are greater than the uniform distance therebetween. In other wordsthe discharge will not tend to occur between a point on the cathode andthe most adjacent point on the anode, but will tend to take placebetween more distant points, and this willv result in variations in thestarting potential voltage. The minimum starting potential distancecorresponds to a path suiciently long to permit a gaseous discharge dueto gas ionization, and while the distance should not be less than thisit may be somewhat greater. I have found that if the spacing is toogreat the initial discharge may also occur between some point on thecathode and a point on the anode afueras@ which is substantiallygreaterthan the shortest path. Accordingly, I prefer an electrode spacing whichis sufciently long to permit a gaseous discharge due to gas ionizationalong the shortest path therebetween, but sufliciently short to preventthe initiation of the discharges along paths substantially greater thansaid constant distance. In one successful embodiment of the inventionthe gas used was argon at a pressure of millimeters of mercury, andthedistance between the cathode screen 6 and the surface of anode 'l wasforty-thousandths of an inch. The getter used in this instance was analloy containing barium and tantalum which when flashed by applyingcurrent to the leads 23 and 24 provides a source of pure barium.

' In operation the same tube will always start at the same voltage incontradistinotion to conventional constructions in which the startingvoltage may vary considerably and has not heretofore in any oase beenless than one volt. This uniformity in starting characteristics is dueto the geometry of the tube by which there is no variation in theeffective distance between any point on the cathode'and the nearestpoint on the anode. Furthermore, irregularity, due to edge effects whichmight result in the discharge seeking to traverse a path greater thanthe uniform distance between the cathode and the anode, is avoided bythe fact that the electrode areas beyond the end caps 8 and 9 areunactivated while this unactivated portion extends in the samegeometrical relationship to the anode as does the activated portion.This provides a uniform field throughout that portion of the space I5between the activated area of the cathode and the adjacent area of theanode. Thus initial discharges through the non-uniform field whichexist, due to edge effects adjacent the upper and lower ends of thecathode and anode, are prevented, since initiation of the discharge atthese unactivated ends does not tend to occur at voltages approachingthe break-down voltage adjacent the activated portions. The dischargemust always occur through uniform distances in uniform fields regardlessof position of the point on the active surface of the cathode at whichthe discharge may be initiated.

The possibility of discharges being initiated through a non-uniformfield at the edges of the cathode and anode is further prevented by thefact that these edges are closed or blocked by the mica plates i9 and20.

In the embodiment of the invention shown in Figs. 4 and 5, numeral 3|indicates a sealed envelope having a reentrant stem 32. Current lead-inwires 33 and 34, sealed in stem 32 by a press 35, provide connectionsbetween a source of power and electrodes 36 and 31.

In this form of the invention the cathode screen 36 is mounted parallelto the fiat anode plate 31, the screen 36 being welded or otherwiserigidly fixed at its peripheral portion to a plate 38. The plate 38 isprovided with opening 39, which opening leaves the central portion ofthe screen 36 uncovered.. while the edges of the screen are shielded bythe peripheral portion of the plate 38. The anode 3l and the cathodesupporting plate 38' are held in spaced parallel relation by means ofinsulating washers 49, having rivets 4| extending therethrough. Theheads of the rivets 4| bear on insulating washers 42 on the outersurfaces of the platesk 3'! and 38. Lead-in wires 43 and M, which aresealed in the stem 32 by the press 35, support a getter 45 in a positionadjacent the outer surface of the screen 36.

" Preferably the plates 31 and 38 are spaced so that the distancetherebetween is substantially equal to the minimum starting potentialdistance for the kind of a gas and the pressure within the envelope 3|.

The manufacture of the device is similar to the mode of manufacturedescribed in connection with the form shown in Figs. 1 3. The screen 36is activated by iiashing the getter i5 to which current may be suppliedby wires i3 and 44. It will be seen that only that portion of the screen36 which is exposed by the opening 39 in the plate 33 will be activated,the remaining portions being shielded by the solid peripheral portion ofthe plate. Thus this structure also provides an arrangement in which thegap between any point on the active cathode area and the anode 31 is thesame as that of any other point. The electrostatic field between theactive area of the cathode and the anode 3l is substantially uniformland distortion of this field at the edges thereof is prevented by theextension of the cathode plate @il and the anode 3l' for some distancebeyond the active area, so that although the active area terminates atthe edge of the opening 39 the electrostatic field continues uniform forsome distance beyond this active area and the distortion at the outeredges of the plates 31 and 38, due to edge effects, does not materiallyaffect the eld in the active area, and discharges in the non-uniform eldat the edges of the plates are prevented since these portions areunactivated.

Although there has been herein described but two embodiments of theinvention, other embodiments within the scope of the. appended claimswill be obvious to those skilled in the art and may be constructed inaccordance with the teachings herein from a consideration of the twoembodiments shown.

What is claimed is:

l. An electric gaseous discharge device comprising a sealed envelopecontaining a gaseous atmosphere, an anode, and a cathode forming withsaid anode agap of substantially a constant distance between any pointon the active surface thereof and the nearest point on said anode, saidconstant distance being not less than the mini- 'mum starting potentialdistance, said cathode having its active area spaced from its ends oredges, providing an inactive area extending for a suflcient distancefrom said active area toY provide an extension of the electrostaticfield beyond said active area, whereby the field adjacent said edges isthe same as the field between said anode and said active surface atpoints remote from said edges, andgaseous discharges along paths greaterthan said constant distance are prevented.

2. An electric gaseous discharge device comprising a sealed envelopecontaining a gaseous atmosphere, an anode, and a cathode forming withsaid anode a gap of substantially a constant distance between any pointon the active surface of said cathode and the nearest point on saidanode, said constant distance being not less than the minimum startingpotential distance, said cathode having its active area intermediate itsends and an inactive area extending in the same spaced relation to saidanode as said active area, said inactive area of said cathode beingseparated from said anode by free space, whereby the electrostatic eldbetween said anode and the active area of said cathode is substantiallyuniform and distortions due to edge effects are eliminated.

3. An electric gaseous discharge device com'- 7 prising a sealedenvelope containing'a gaseous atmosphere, an anode, and a cathode, thedistance between any point on the active area of said cathode and thenearest point on said anode being substantially equal to the minimumstarting potential distance for the pressure and kind of gas.

within said envelope, said cathode having said active area intermediatethe ends thereof and an inactive area extending in the same spacedrelation to said anode as said active area, said inactive area of saidcathode being separated from said anode by free space, whereby theelectrostatic eld between said anode and the active area of said cathodeis substantially uniform and distortions due to edge eiTects areeliminated.

4. An electric gaseous discharge device comprising a sealed envelopecontaining a gaseous atmosphere, an anode, and' a cathode, the dis-`tance along any line of force between the active area of said cathodeand said anode through free space in said tube being substantially equalto the minimum starting potential distance for the pressure and kind ofgas within said envelope, said cathode having said active areaintermediate the ends thereof and an inactive area adjacent the saidends, said inactive area extending in the same spaced relation to saidanode as said active area, said inactive area of said cathode beingseparated from said anode by free space, whereby the electrostatic eldbetween said anode and the active area of said cathode is substantiallyuniform and distortions due to edge effects are eliminated.

5. An electric gaseous discharge device including a sealed envelopecontaining an anode cornprising a cylindrical member, a cathodecomprising a cylindrical member having an activated intermediate portionand unactivated end portions, said anode and cathode beingconcentrically arranged one within the other and spaced to provide a gapof constant distance between any point on the active surface of thecathode and the nearest point on the anode, said unactivated endportions of said cathode extending in the same spaced relation to saidanode as said acti-- to the minimum starting potential distance for.

the pressure and kind of gas within said envelope, said cathode havingan active area intermediate the ends thereof and an inactive areaextending in the same spaced relation to said anode as said active area,said inactive area of said cathode being separated from said anode byfree space, whereby the electrostatic field between said anode and theactive area of said cathode is substantially uniform and distortions dueto edge eects are eliminated.

PAUL W. STUTSMAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

vUNITED STATES PATENTS Number Y Name Date 1,545,207 Smith July '7, 19251,731,889 Donle Oct. 15, 1929 1,803,985 Walker May 5, 1931` 2,083,545Braselton July 27, 1937 2,141,654 Kott Dec. 27, 1938 2,195,913 BachmanApr. 2, 1940 2,256,101 Muller Sept. 16, 1941 1,948,720 Knowles Feb. 2'7,1934

